This application claims the benefit of co-pending U.S. provisional patent application serial No. 60/327,260 filed on Oct. 5, 2001 for DUCT CLEANING WITH PULSE VALVE, the entire disclosure of which is fully incorporated herein by reference.
The invention relates generally to apparatus and methods for removing powder from powder conveying elements in a powder coating spray system. More particularly, the invention relates to methods and apparatus for removing powder that has adhered to interior surfaces or collected within interior regions of a powder transfer duct by incorporating a pulse valve or other device for applying a high volume high pressure discharge of air into the duct to dislodge the powder. The invention may conveniently be used, for example, in quick color change systems.
Powder coating spray systems for applying a powder coating to objects typically include a partially enclosed powder spray booth and one or more powder spray guns. Various spraying technologies have been developed including electrostatic and non-electrostatic spraying. Regardless of the spraying technology used, a substantial quantity of powder overspray is usually generated because not all of the sprayed powder adheres to the target surface. This overspray powder is then recovered typically using some form of a filtering system because the overspray powder tends to be airborne or easily entrained into an air stream. A common powder recovery system utilizes one or more cyclone separators to filter powder entrained in an air flow.
Overspray powder is entrained in an air flow produced by operation of the cyclone separator, with the entrained powder being transferred from the spray booth to the cyclone separator via a powder transfer duct. Because the powder is traveling at a fairly high speed through the duct, it tends to adhere to portions of the interior surface of the duct due to impact. Eddy current effects may also cause powder to collect in corners or other interior regions of the duct. This trapped powder must be cleaned out of the duct as part of a color change operation.
Compressed air injectors are known to be used within an air flow conduit to assist in the entrainment of powder in the air flow stream, such as is shown in U.S. Pat. No. 5,906,676 issued to Drummond. The injector however directs pressurized air generally parallel to the conduit walls in order to augment air flow, not for dislodging trapped powder within the duct.
Typically, to clean the duct for color change, a cover or access door to the duct must be opened and an air wand or other manual air spray device is used to blow the powder off the interior duct surfaces. These manual cleaning operations are unsuitable for automatic or quick color change applications.
The need exists therefore to provide method and apparatus for removing powder in a duct without requiring manual spraying operations to improve speed for a quick color change powder spraying system.
In accordance with one aspect of the invention, a pressurized volume of air is directed at an interior surface of a powder transfer duct to dislodge powder particles adhering thereto. In one embodiment of the invention, the duct is a passageway for powder that is entrained in a primary air stream from a powder spray booth to a powder collection device such as, for example, a cyclone separator. In this embodiment, the pressurized air is provided by a device that can be selectively activated to direct a blast of high pressure air into the duct interior. In one specific embodiment, the device is realized in the form of a pulse valve that has an outlet that opens to the duct interior and directs a pulse of pressurized air at a surface or region within the duct where powder tends to accumulate, either from eddy current effects or from impacting the interior surfaces. The pulse valve may be mounted, for example, to a wall of the duct. Pressurized air is supplied to the pulse valve from a source such as an accumulator connected thereto. The pulse valve may be manually actuated or actuated by other suitable control mechanisms. In accordance with another aspect of the invention, the device is activated while air is flowing through the duct, such as when the cyclone separator is operating. In this circumstance, the dislodged powder becomes entrained in the primary air stream and is discharged to the cyclone separator.
In accordance with the invention, a method for cleaning a powder transfer duct is also provided. In one embodiment of the invention, a pressurized volume of air is injected into the duct at a location so as to direct the pressurized air at an interior surface or region of the duct to dislodge powder that is trapped in the duct. By blowing off the powder while the duct has a primary air stream flowing therethrough, the dislodged powder is removed from the duct.
These and other aspects and advantages of the present invention will be readily appreciated and understood from the following detailed description of the invention in view of the accompanying drawings.